Although indium arsenide (InAs) exhibits extremely high electron mobility, and should thus be particularly suitable for use in high sensitivity magnetic sensors, the following problems relating to its fabricating process and its characteristics exist;
(1) It is very difficult to grow a thin indium arsenide film having good crystallization and high electron mobility.
(2) the temperature characteristics of InAs when used as a magnetic sensor deteriorate at high temperatures due to the narrow band gap of the indium arsenide.
Attempts have been made to grow thin films of indium arsenide on various types of substrate. However, due to the large difference between the lattice constant of the indium arsenide and that of the insulating substrate on which the single crystal thin film of InAs is grown, lattice mismatch occurs near the interfacial boundary between the indium arsenide and the substrate itself. This results in low electron mobility so that adequate electron transport characteristics cannot be achieved. The resultant film is also susceptible to large changes in its characteristics during the fabricating process of the element, and there is also a tendency for the resistance temperature characteristics to be poor. Consequently, magnetic sensors wherein the magnetic sensing portion has a thin indium arsenide film, have a low electron mobility, making the fabrication of a high sensitivity magnetic sensors difficult.
In order to improve the temperature characteristics of the indium arsenide, tests have been made with a ternary alloy doped with gallium (Ga) to broaden the band gap. In this case indium phosphide (InP) having the same lattice constant as the InGaAs was used as the insulating substrate. In these tests, the composition ratio of In and Ga used to match the lattice of the InP was only In.sub.0.53 Ga.sub.0.47 As, and there was no insulating substrate corresponding to an arbitrary composition of InGaAs. As a result, even with the thin film growth of the InGaAs having a different lattice constant from that of the InP, as with the InAs, it was not possible to suppress the lattice mismatch occurring in the interface of the substrate. A high electron mobility thin film of InGaAs was therefore difficult to obtain. Furthermore, to obtain a high sheet resistance, it is necessary to have a thin layer. However due to the lattice mismatch inherent with a thin layer, it is difficult to control the carrier density. As a result, it is difficult to obtain a thin InAs film having the high electron mobility and high sheet resistance desirable for a magnetic sensor.
Present day technology related to magnetic sensors using InAs thin film as a magnetic sensing layer is disclosed in examined Japanese Patent Publication No. 2-24033, and unexamined Japanese Patent Laying-open Nos. 61-20378 and 61-259583. Examined Japanese Patent Publication No. 2-24033 proposes a Hall element wherein element temperature characteristics are improved by doping the magnetically sensitive layer of InAs with S, Si. With this element however, there is a drop in element resistance at high temperatures over 100.degree. C., so that the element is not reliable for use at high temperatures as a Hall element. Unexamined Japanese Patent Laying-open No. 61-20378 proposes a Hall element having a magnetically sensitive crystalline layer of InAs or InGaAs grown on a semi-insulating GaAs substrate. With this element however there is lattice mismatch at the interface between the GaAs substrate and the InAs layer so that acceptable reliability and sensitivity cannot be obtained at high temperatures. Moreover, unexamined Japanese Patent Laying-open No. 61-259583 proposes a Hall element having a magnetically sensitive layer of InAs grown on a sapphire substrate. With this element however, a drop in element resistance was observed at high temperatures over 100.degree. C. making this element also unreliable for use at high temperatures. Up until now we have therefore required different fundamental technology to realize magnetic sensors having very high sensitivity. Furthermore, this search does not stop with magnetic sensors, but is also applicable to the field of light, pressure and strain detection, and is aimed at the realization of detectors having high reliability and sensitivity in spite of miniaturization.